1. Technical Field
The present invention relates to solar cells, and more particularly to devices and methods which employ a barrier layer between p-type layer formation and intrinsic layer formation.
2. Description of the Related Art
Fabrication of amorphous hydrogenated silicon (a-Si:H) solar cells is performed with the deposition of constituent active layers. The active layers include a p-type layer (or p-layer), an intrinsic layer (or i-layer) and an n-type layer (or n-layer), collectively a p-i-n or pin stack.
In some processes, a surface of the active layer is exposed to reactant by-products that may be present in the chamber or may be left over from previous processing. While solar cell fabrication using a single chamber is manufacturing friendly, this process suffers from the drawback of different species of elements or compounds being left over from previous processing. For example, when diborane is used for a p-type dopant source (e.g., boron), boron is left over in the chamber. If further processing is conducted in the same chamber a higher probability of contamination occurs, which can result in poor device performance.
In another example, trimethylborane(TMB) may be employed as a p-type dopant source. In this case, less boron is left over after depositing p-type a-SiC:H. However, for other materials, e.g., a-Ge:H, a-Si:H, etc., it is extremely difficult to provide boron to these films without contaminating reactants being present (the process is not flexible for all device materials). These contaminants usually settle at interfaces and affect device performance.